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A new National Climate Assessment Draft Report has been issued by The National Climate Assessment and Development Advisory Committee (NCADAC). NCADAC is an interagency group responsible for providing the federal government with periodic reports summarizing what is known about climate change and how it will affect the United States. Their last report was in 2009.

The report is a draft, and will undergo revision before final publication some time in 2013. However, as it is based on reviews of peer-reviewed and published data, it is unlikely that the “meat” of the report will change substantially. Generally, I try to deemphasize predictions in this blog, focusing instead on actual findings. However, this report is sufficiently important that it can’t just be ignored. The report doesn’t focus on Missouri, but it does discuss the Midwest, and Missouri is the southernmost state in that region. I’ve copied two graphics from the report at right. The first concerns heat, the second concerns precipitation.

Figure 18.2: Temperature Details Show a Range of Changes. Increasing annual average temperatures (top left) by the mid-?century (2041-2070) as compared to the 1971-2000 period tell only part of the climate change story. Maps also show projected increases in the number of the hottest days (days over 95°F, top right), longer growing seasons (bottom left), and an increase in cooling degree days (bottom right). Projections are from Global Climate Models that assume emissions of heat-trapping gases continue to rise (A2 scenario).

The story on heat is simple: it is predicted to get warmer, perhaps dangerously warmer. As noted in the previous post Missouri Roasts in 2012, the average temperature in Missouri has already warmed. But that is just the beginning. At right is a graphic from the report that shows predictions for what might happen by mid-century to average temperatures, the number of days with high temperatures above 95°, the length of the frost-free season, and the number of yearly cooling degree days. The number of days with high temperatures above 95° are predicted to increase by more than 25. In St. Louis, since 1874, the average number of days with highs above 90° was 42, while the average number of days with highs above 100° was 3 (data for 95° not reported). Thus, an increase of 25 would represent something around a doubling. Extremely hot weather is associated with many negative effects, including reduced agricultural yields, problems with water quality, problems with air quality, increased rates of respiratory illness, and even death.

Cooling degree days is a measure of how much people will need to use their cooling systems. It indicates how many days had average temperatures above 65°F, and how high above. For instance, if the average temperature on a given day is 70°, that represents 5 cooling degree days. Cooling systems are large consumers of electricity, and they are responsible for spikes in electrical demand that occur on sunny, hot summer days. These spikes emit large amounts of GHG and threaten to overburden the electrical grid, risking brownouts or even blackouts. The graphs shows that the number of degree days in Missouri will increase by more than 600 in some regions, and more than 750 in others (the long term average for Missouri is just over 6600, so this represents about a 10% increase).

The story on precipitation is more complex.On a yearly basis, the Midwest is actually predicted to have an increase in precipitation. However, more of it is predicted to occur in heavy downpours, meaning there will be longer dry periods between. And as the graphic from the report copied at right shows, precipitation is predicted to increase during the winter and spring, but decrease during the summer. The summer decrease is substantial, 10-20% across the state.

Figure 2:12: Projected Precipitation Change by Season. Projected percent change in season precipitation for 2070-2099 (compared to the period 1901-1960) under an emissions scenario that asummes continued increases in emissions (A2). Teal indicates precipitation increases, and brown, decreases.

Increased heat, including an increase in extremely hot weather, plus reduced precipitation during the summer, plus longer periods between intense downpours: these trends imply summer drought. Drought is difficult to predict, as it depends on many very complex variables. The National Climate Assessment Draft Report discusses drought, but does not make specific drought predictions relevant to Missouri. It is one of many negative effects that might occur that we simply are not yet able to pin down.

The report is almost 1200 pages long, and it covers many topics that I’m not going to get into. Those who want to read it and/or review and offer comments should follow the link below to the NCDC website.

For extremely high temperatures in St. Louis, Ranked Occurrences of Temperatures >= 90 and 100 Degrees (1893-present), Climatology and Weather Records, National Weather Service, St. Louis, MO, http://www.crh.noaa.gov/lsx/?n=cli_archive.